1. Field of the Invention
The present invention provides a method for providing subscribers of a wireless communication network with multiple points of connectivity without adding additional hardware to the network or to the subscriber's mobile.
2. Description of the Related Art
Wireless communication networks have established well known techniques that provide multiple subscribers access to these networks. Some of these techniques include Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA). Also, various combinations of these techniques (and other multiple access techniques) are used to provide access to subscribers. As the use and popularity of these networks have increased, the type of services and resources provided to subscribers have changed and increased in complexity. The resources are the system equipment (e.g., radio transmitters, radio receivers, processing equipment) usually owned and operated by a service provider. The resources are also various capabilities provides by the system equipment such as the bandwidth allocated to a particular subscriber, the power at which a subscriber is allowed to transmit its communication signals or the rate at which a subscriber is allowed to receive and transmit information. The services are the ability of any one subscriber to use the resources in a variety of ways. Traditionally, wireless communication networks allowed subscribers to communicate with each other and with other communication networks via voice channels; that is, the main type of communication was voice communications between subscribers or between subscribers and other networks.
However, with the advent of the Internet and other data networks, wireless communication networks have had to provide services not only for voice but also for data. The data are usually in the form of digital information that represent communication signals for text, graphics, video and other signals including voice. Various protocols have been created to accommodate the transmission and reception of data over wireless communication networks. Each protocol is a particular set of rules that dictates how communications between subscribers are to be initiated, maintained and terminated. The protocols also dictate the manner of communications between subscribers and system equipment and communications between subscribers and other networks. Communication signals originating from system equipment are used to implement the various steps of a protocol; these communication signals are typically referred to as system information or signaling information. Many of these protocols have been established into standards that are followed by communication networks throughout various parts of the world.
Referring to FIG. 1, there is shown a typical wireless communication network infrastructure which complies with standards for particular CDMA data networks called CDMA 2000 networks. A subscriber, represented by wireless laptop 148, is migrating within the network. The subscriber and/or its equipment (i.e., subscriber equipment) will hereinafter be referred to as a Mobile Node (MN). An MN is typically owned and operated by a subscriber of the communication network. An MN can be, for example, a cellular phone, a wireless laptop PC or a wireless Personal Digital Assistant (PDA). The MN typically gains access to the network via an air interface between the MN and a network attachment point. A network attachment point is the system equipment that communicates directly with an MN and facilitates access to the communication network for an MN. Access to a network involves confirming that an MN is authorized to use the resources of the communication network and allowing the MN to use available resources upon such confirmation. The air interface defines the signaling information to be exchanged between an MN and the BTS (over a communication channel between MN and BTS) and resources to be allocated to the MN to give the MN access to the network.
In FIG. 1, a network attachment point is a BTS or a set of BTS's (e.g., BTS 120, 122, 124, 126, 128, 130, 132 and 134) which contain radio transmitters and receivers (not shown) used to transmit and receive MN and system communication signals. Each BTS serves a particular cell where each cell is symbolically represented by a hexagon. For example, cell 114 is being served by BTS 134. Each cell delineates the geographical boundaries within which an MN can receive and/or transmit communication signals to a BTS. In many networks, such as the one depicted in FIG. 1, the cells are divided into sectors whereby each sector represents a particular geographical area being served by particular resources of the BTS. For ease of illustration, each cell is shown to be divided into six sectors. It will be readily understood that the number of sectors in a cell depends on the particular resources contained in the BTS serving the cell and thus a cell may be divided into more or less than six sectors.
Each BTS is coupled to a Base Station Controller (BSC) via a network communication link. A BSC can be coupled to more than one BTS; for example, BSC 138 is coupled to BTS 120, 122, 124 and 126. The BSC's are examples of network controlling elements which are system equipment that manage the network attachment points (e.g., BTS's) to which they are coupled; that is, the BSC's dictate how and when certain communication signals are to be transmitted and/or received by a BTS or a set of BTS's. Thus, a BSC services and controls the MN. For example, a BSC instructs a BTS as to the power level at which the BTS is to transmit its communication signals to the MN. Information exchanged between a BSC and a BTS is performed in accordance with a standard being followed by the communication network. The BSC's are coupled to each other via communication links (not shown). Each BSC is also coupled to a Packet Data Serving Node (PDSN) which serves as a gateway between the wireless communication network and a data network (not shown) such as the Internet; that is, the data network is coupled to the wireless communication network via the PDSN. The PDSN's serve a certain geographical area within which the cells of the corresponding BTS's are located. Referring to FIG. 1 PDSN 1 (i.e., system equipment 146) serves a certain area denoted by the dashed lines; similarly, PDSN2 and PDSN3 have their own serving areas. The PSDN is a type of data service entity, which not only serves as a gateway to a coupled data network, but also allows a subscriber of the wireless communication network to use the available services of the coupled data network.
For certain applications, a MN requires the use of a persistent IP address in the data network coupled to a PDSN. The IP address is a specific label that specifically identifies the MN regardless of which data network is exchanging information with the MN. A persistent IP address means that as the user moves geographically and connects to a new PDSN, the data network will route the user's packets while maintaining the same user address to the current PDSN even though the user is not in an area of the data network that would usually be able to route such a packet given the address of the packet. One example of a protocol that allows this service is Mobile Internet Protocol (IP) [Request For Comment 2002]. The MN invokes Mobile IP procedures by registering with the PDSN as part of initialization with the PDSN. Initialization with the PDSN is the set of procedures required for the MN to obtain service on the PDSN. Mobile IP has two styles of data network mobility (i.e., transferring from one data network location to another data network location), one in which the PDSN participates directly in the data network mobility function, and another in which the mobile itself performs data network mobility functions. There are other types of data network mobile routing protocols as well, such as General Packet Radio Service (GPRS) and Cellular Digital Packet Data (CDPD). All of these protocols will route information to a PDSN which is then able to deliver the information to the MN.
Some or all of the BSC's may also be coupled to Mobile Switching Centers (MSC) (not shown) which provide access to the Public Switched Telephone Network (PSTN). Each MSC typically manages a region comprising several BTS's. Therefore, each set of BTS is controlled by one BSC (and perhaps one MSC) which is coupled to one or more PDSN that provides access to a data network. Although FIG. 1 shows a one to one relationship of BSC's and PDSN's in many cases a service provider would have an architecture where a plurality of BSC's are connected to a plurality of PDSN's to provide load balancing or fault tolerance in the event a PDSN fails.
Information transmitted by an MN is received by multiple BTS's coupled to the same BSC. Thus the information received by each BTS is identical. Each BTS transfers its received information to the same BSC which formats the information into a block called an octet stream. The octet stream is then transferred to the PDSN coupled to the BSC and the PDSN transfers the octet stream to the coupled data network. In short, the MN is given access to the data network coupled to the multiple BTS's via the BSC and PDSN.
Wireless communication networks such as the one depicted by FIG. 1 suffer from the limitation that, for a particular MN, only one access point to a data network at a time is allowed. Due to the increased demand to gain access to data networks (as explained above), subscribers often desire simultaneous access to different networks. The networks can be private data networks, public data networks (e.g., the Internet) or voice networks such as the PSTN. Also, information being transmitted and received by an MN having access to a data network is often quite sensitive to interruptions in service caused by handoffs being performed by the wireless communication network. The interruptions are often due to loss of information that occur during handoffs. Particular types of information—such as information associated with multimedia applications—are especially sensitive to loss of information that can occur to handoffs.
A handoff is a well known procedure whereby a migrating MN being served by a particular BTS is physically located such that the BTS cannot provide adequate quality of service to the MN. The BSC controlling the serving BTS at some point will decide to transfer (i.e., “hand off”) its service and associated control of the MN to another BSC in control of another set of BTS's (i.e., new set of BTS's) more adequately able to provide the services required by the migrating MN. Because this handoff is between BSC's, this handoff is often referred to as a hard handoff. Still, referring to FIG. 1, if the MN (e.g., laptop 148) moved from BTSs controlled by BSC1 (144) to the set of BTS's controlled by BSC 2 (136), a handoff is also required between the corresponding PDSN's (i.e., handoff between PDSN 1 (146) and PDSN 2 (136)). Now, if the MN desires the same persistent address on PDSN 2 as the MN had on PDSN 1, the MN must register with PDSN 2 using data network mobile routing protocol such as Mobile IP, as discussed above. A user may desire the same address so as to not disrupt current communication flows, or so that the user may be reached via a known and static address anywhere in the data network. As part of this process, the mobile must re-establish communications with PDSN 2 via negotiation as well as authenticate (confirm its authorization to use the network) itself to the network. The PDSN may contact other network equipment to complete authentication and authorization of the MN, and may invoke security protocols to protect the MN's communications. As explained above the PDSN may directly participate in the data network mobile routing protocols or may simply be an intermediary between the network and the mobile.
An MN can be handed off from one BTS to another several times during a session depending on the location and speed of the MN relative to the BTS's of the network. A session is the amount of time elapsed during which an MN has obtained access to the network, engaged in communications by using resources provided by the network and terminated the particular communications. A Selection and Distribution Unit (SDU) (not shown), which is usually part of a BSC, chooses the BTS that is to serve a migrating MN prior to handoff. The SDU typically chooses a BTS based on the transmitting power level of an MN's communication signals being received by a candidate BTS and the information rate at which the MN is conveying information. During the handoff, the controlling BSC transfers signaling information and other data associated with a handoff protocol to the new BSC so that the new BSC can control its BTS to properly serve the MN.
During such transference of data, service to the migrating MN is interrupted causing information being transmitted or received by the MN to be lost. There are two types of interruptions that cause information loss. One interruption occurs while the radio equipment in the MN reconfigures itself to receive radio signals from the new BTS. While the radio in the mobile reconfigures its radio receivers, it does not receive information. The interruption due to radio reconfiguration is relatively short and is typically on the order of a fraction of a second. The other interruption is the information loss that occurs while the MN registers and initializes with the new PDSN. As outlined above, registration and initialization with the new PDSN (e.g. PDSN 2) implies various protocol procedures such as data link initialization, authentication, authorization, and accounting, security procedures, and mobile routing in the data network. While the second PDSN (e.g. PDSN 2) performs these functions, information is routed to the previous PDSN (e.g. PDSN 1). This second interruption is much longer and is the cause of the majority of loss of information for the mobile. The amount of delay that occurs due to the execution of the data link layer initialization, Mobile IP, AAA, and security functions may be several seconds.
It should be noted that a handoff can also be initiated by a MN whereby the MN is configured to monitor the quality of signals from the network and then decide when a handoff is warranted. In such a case the MN informs the network of the need for a handoff and the network then executes the handoff as described above.
Multiple point connectivity, which is the ability of an MN to simultaneously have access to multiple networks (e.g., data networks) coupled to the wireless network via data service entities (e.g., PDSN's), would require that additional hardware and software be added to the MN. Examples of the additional hardware are transmitters, receivers, modulators and other circuitry typically used to process communication signals. Such additional resources would not only allow multiple point connectivity, but would significantly, if not virtually, eliminate interruptions (and thus loss of data) due to handoffs.
In such cases, the network would be able to hand off an MN from one BTS to another with relatively little or no loss of data. That is, an MN would have previously established a first session with a first set of BTS's being controlled by a first BSC coupled to a first PDSN. During the time that the mobile communicates with the first set of BTSs, the mobile monitors radio signals from other sets of BTSs. When the mobile or network detects that the quality of the radio signal from the first set of BTSs has degraded to a point that further degradation would cause an unsatisfactory communication quality or even loss of a session, the mobile then establishes a second and identical session with a second set of BTS's under the control of a second BSC coupled to a second PDSN. Each session is handled by a different set of hardware (e.g., radio transmitter and receiver) within the MN. After establishing data service on the second PDSN, the MN would drop the first session—and thus the first set of BTSs. Because the mobile engaged in this “make before break” handoff procedure, the mobile would experience relatively little or no loss of communication.
Currently, for CDMA networks, an MN is capable of opening multiple simultaneous instances of a Radio Link Protocol. The RLP is a protocol that dictates how a network is to provide multiple resources to a single MN where such resources are being provided by a particular set of BTS's controlled by a particular BSC. Each instance of an RLP, which is likened to a communication channel, is governed and established by data stored in an origination message sent by an MN or by a BSC of the network while establishing a session between the MN and the network. The origination message also contains information indicating the type of service to be provided by the network during the session. Thus, an MN can be transmitting and/or receiving a first type of information through one instance of RLP and transmitting and/or receiving a second type of information through another instance of RLP. Because each of the instances of RLP are routed through the same set of BTS's—and thus the same BSC and PDSN—the MN does not have simultaneous access to different networks. As stated previously, the information from the various instances of RLP are combined as an octet stream and sent to a single PDSN. The octet stream is divided into 20 ms frames which are transmitted and received by the MN and controlling BSC. The amount of information contained in a frame is dependent on the rate at which the information is being conveyed between an MN and the destination network. To achieve multiple point connectivity with the use of additional hardware and software in the MN would require the redesign and manufacture of wireless subscriber and system equipment. Such an approach would mandate substantial changes in the standards currently being used by wireless networks. Most importantly, the cost of adding new hardware to subscriber and system equipment is most likely quite prohibitive to subscribers and system providers.
What is therefore needed is a method for providing multiple points of connectivity to subscribers of wireless communication networks without having to add new hardware to subscriber and system equipment whereby such method can be implemented within the context of the communication standards which are being followed by the communication networks. In the context of the communication network depicted by FIG. 1, it would be desirable for an MN of such a network to have multiple instances of RLP simultaneously where each instance is associated with a different network controlling element (i.e., a different BSC).